1. Field of the Invention
The present invention pertains to a liquid crystal display device and particularly relates to a technology that is effectively applied to a compact liquid crystal display device.
2. Description of the Related Art
Thin-film transistor (TFT) liquid crystal display devices that include a compact liquid crystal display panel that is a color display and whose number of sub-pixels is about 240×320×3 are widely used as display portions in mobile devices such as mobile telephones.
Usually, a liquid crystal display device includes a liquid crystal display panel and a backlight that illuminates the liquid crystal display panel with light, but in a liquid crystal display device that is used as a display portion in a mobile device such as a mobile telephone, the back light is configured by a resin mold frame (below, called a “mold”), an optical sheet group and a light guide plate that are disposed inside the mold, and a reflection sheet that is disposed on the underside of the light guide plate.
In recent years, a structure where the bottom surface of the mold is omitted is becoming mainstream among liquid crystal display devices for mobile telephones due to the demand to make the liquid crystal display devices thin (see patent citation 1 (Japanese Patent Application Laid-Open Publication No. 2007-25484)).
FIG. 8A, FIG. 8B, FIG. 9A and FIG. 9B are cross-sectional diagrams of relevant portions showing conventional structures of a liquid crystal display device. FIG. 8B and FIG. 9B are diagrams showing a cross-sectional structure on a long side, and FIG. 8A and FIG. 9A are diagrams showing a cross-sectional structure on a short side where a semiconductor chip is mounted.
Turning now to these drawings, 1 is a resin mold frame, 2 is an optical sheet group (a lower diffusion sheet, two lens sheets, an upper diffusion sheet), 3 is a light guide plate, 4 is a reflection sheet, 5 and 6 are glass substrates, 7 is an upper polarization plate, 8 is a lower polarization plate, 9 and 10 are double-sided tapes, 11 is a semiconductor chip (a driver), 12 is a flexible wiring substrate, 13 is a spacer, 15 is white light-emitting diodes, and 16 is a flexible wiring substrate on which the white light-emitting diodes 15 are mounted.
In the conventional structure example shown in FIG. 8A and FIG. 8B, a liquid crystal display panel, which has the largest mass in the liquid crystal display device, is fixed to the resin mold frame 1 by the double-sided tape 10. Further, the reflection sheet 4 is fixed to the resin mold frame 1 by the double-sided tape 9.
The conventional structure example shown in FIG. 8A and FIG. 8B is a structure where the peripheral portion of the lower glass substrate 6 of the pair of glass substrates 5 and 6 that configure the liquid crystal display panel is fixed to the resin mold frame 1 by the double-sided tape 10 and where the lower polarization plate 8 is dropped into the inside of the resin mold frame 1 (below, called a “lower polarization plate dropped structure”). This lower polarization plate dropped structure is suited to making the liquid crystal display device thin.
The conventional structure example shown in FIG. 9A and FIG. 9B is a structure where the periphery of the lower polarization plate 8 of the liquid crystal display panel is fixed to the resin mold frame 1 by the double-sided tape 10 (below, called a “lower polarization plate fixed structure”). In this structure, the double-sided tape 10 also holds the inside optical sheet group 2. This lower polarization plate fixed structure adheres, while holding from above, the periphery of the optical sheet group 2 to the liquid crystal display panel, so it can deter problems such as ingression of foreign matter into the inside of the optical sheets and shifting of the optical sheets.